According to this article from 2015 How much oil is left on Earth
1.5 trillion barrels of crude oil reserves were left in the world by end 2015
But how much oil was already consumed worldwide since it was started to use massively in the mid 19th century? Is it most of it or a small part of it?
PS: I'm not sure if this question is for Earth Science SE or for Economy SE, if you think it's in the wrong SE please move it.